On Complex Source Code Reading Strategy

Hello Dear PostgreSQL Hackers,

I want to be PG hacker but it seems a complex beast to find my way out in it.
So, can anyone suggest me from his experience/style the general
approaches/techniques/strategies on how to read complex source code in
general and PG in particular effectively.

Can you remember your being novice to PostgreSQL hacking and write
your experience/style to me and probably to other novices as well.

There are some guidelines in PG wiki but they are far from the truth
of down the rabbit hole.

I believe that there is plethora of knowledge and skill sets in the PG
hackers head not to be found in any kind of written material and thus,
that It would be great if any PG hacker could write his
experience/style of PG hacking so that is of useful asset for PG
hacking beginners.

Regards,
Zeray